Radiation detection system including a scintillating material and an optical fiber and method of using the same

ABSTRACT

A radiation detection system can include optical fibers and a material disposed between the optical fibers. In an embodiment, the material can include a fluid, such as a gas, a liquid, or a non-Newtonian fluid. In another embodiment, the material can include an optical coupling material. In a particular embodiment, the optical coupling material can include a silicone rubber. In still another embodiment, the optical coupling material has a refractive index less than 1.50. In still another embodiment, the radiation detection system can have a greater signal:noise ratio, a light collection efficiency, or both as compared to a conventional radiation detection system. Corresponding methods of use are disclosed that can provide better discrimination between neutrons and gamma radiation.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority under 35 U.S.C. §119(e) to U.S. PatentApplication No. 61/356,352 entitled “Radiation Detection SystemIncluding a Scintillating Material and an Optical Fiber and Method ofUsing the Same,” by Menge, filed Jun. 18, 2010, which is assigned to thecurrent assignee hereof and incorporated herein by reference in itsentirety.

FIELD OF THE DISCLOSURE

The present disclosure is directed to radiation detection systemsincluding scintillating materials and optical fibers and methods ofusing the same.

BACKGROUND

Radiation detection systems are used in a variety of applications. Forexample, scintillators in the radiation detection systems can be used todetect neutrons and gamma radiation. Such radiation detection systemsare used by security agencies to detect radioactive or other hazardousmaterials, particularly at national borders, airports, and shippingdocks.

FIG. 1 includes an illustration of a cross-sectional view of aconventional radiation detection system 10 that includes a scintillatingmaterial 12 that produces scintillating light in response to thermalneutrons. The scintillating material 12 includes ⁶LiF and ZnS:Agparticles within a polymer matrix. Thermal neutrons cause thescintillating material to emit light that is received by wavelengthshifting fibers 14. The wavelength shifting fibers 14 include apolystyrene core 144 surrounded by a poly(methyl methacrylate) cladding142. Epoxy 16 is an optical coupling material that lies between thescintillating material 12 and the wavelength shifting fibers 14 andbetween the fibers 14 themselves. Blue light is emitted by thescintillating material 12 that is shifted to green light by thewavelength shifting fibers 14. A relatively low fraction of the greenlight is received by one or more photomultiplier tubes (notillustrated).

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure may be better understood, and its numerousfeatures and advantages made apparent to those skilled in the art byreferencing the accompanying drawings.

FIG. 1 includes an illustration of a cross-sectional view of a portionof a conventional radiation detection system. (Prior art)

FIG. 2 includes an illustration of a perspective view of a portion of aradiation detection system in accordance with an embodiment describedherein.

FIG. 3 includes an illustration of a cross-sectional view of a portionof a radiation detection system including optical fibers withoutcladding in accordance with a particular embodiment.

FIG. 4 includes an illustration of a cross-sectional view of a portionof a radiation detection system including optical fibers, wherein afluid is disposed between the optical fibers in accordance with anotherparticular embodiment.

FIG. 5 includes an illustration of a cross-sectional view of a portionof a radiation detection system including optical fibers and an adhesivelayer between the optical fibers and an optical coupling material inaccordance with a further particular embodiment.

FIG. 6 includes an illustration depicting loss of photons at S-shapedbends for different radiation detection systems.

FIG. 7 includes a graph of light collection efficiency as a function ofbend ratio for different radiation detection systems.

The use of the same reference symbols in different drawings indicatessimilar or identical items.

DETAILED DESCRIPTION

The following description in combination with the figures is provided toassist in understanding the teachings disclosed herein. The followingdiscussion will focus on specific implementations and embodiments of theteachings. This focus is provided to assist in describing the teachingsand should not be interpreted as a limitation on the scope orapplicability of the teachings. While numerical ranges are describedherein to provide a better understanding of particular embodiments,after reading this specification, skilled artisans will appreciate thatvalues outside the numerical ranges may be used without departing fromthe scope of the present invention.

As used herein, the terms “comprises,” “comprising,” “includes,”“including,” “has,” “having,” or any other variation thereof, areintended to cover a non-exclusive inclusion. For example, a process,method, article, or apparatus that comprises a list of features is notnecessarily limited only to those features but may include otherfeatures not expressly listed or inherent to such process, method,article, or apparatus. Further, unless expressly stated to the contrary,“or” refers to an inclusive-or and not to an exclusive-or. For example,a condition A or B is satisfied by any one of the following: A is true(or present) and B is false (or not present), A is false (or notpresent) and B is true (or present), and both A and B are true (orpresent).

Also, the use of “a” or “an” is employed to describe elements andcomponents described herein. This is done merely for convenience and togive a general sense of the scope of the invention. This descriptionshould be read such that the plurals include one or at least one and thesingular also includes the plural, unless it is clear that it is meantotherwise. For example, when a single item is described herein, morethan one item may be used in place of a single item. Similarly, wheremore than one item is described herein, a single item may be substitutedfor that more than one item.

Unless otherwise defined, all technical and scientific terms used hereinhave the same meaning as commonly understood by one of ordinary skill inthe art to which this invention belongs. The materials, methods, andexamples are illustrative only and not intended to be limiting. To theextent not described herein, many details regarding specific materialsand processing acts are conventional and may be found in textbooks andother sources within the scintillating and radiation detection arts.

As will be described herein, radiation detection systems can be designedand fabricated to improve signal:noise ratio as compared to conventionalradiation detection systems, such as the radiation detection system thatis partially illustrated in FIG. 1. Particular embodiments can reducephoton transmission loss for S-shaped bends, improve light collectionuniformity between optical fibers, improve light collection efficiencyof optical fibers, or any combination of these properties. Theparticular embodiments are described in more detail below and are usedto illustrate some embodiments. After reading this specification,skilled artisans will appreciate that other embodiments can be usedwithout departing from concepts as described herein.

FIG. 2 includes an illustration of a perspective view of a portion of aradiation detection system 20 that includes a scintillating material 22,optical fibers, such as optical fibers 242, 244, and 246, andphotosensor modules 26. The scintillating material 22 can be configuredto produce scintillating light in response to receiving a targetradiation, such as a neutron, gamma radiation, other target radiation,or any combination thereof. The scintillating light produced by thescintillation material 22 can include visible light or other radiation(such as ultraviolet radiation). The optical fibers are opticallycoupled to the scintillating material 22. In the embodiment asillustrated, the optical fibers receive scintillating light from thescintillating material 22 and transmit such light or wavelength-shiftedlight to the photosensor modules 26. In a particular embodiment, thescintillating light is blue, and the optical fibers shift the wavelengthsuch that green light is received by the photosensor modules 26.Although not illustrated, the radiation detection system 20 can includea microprocessor, a microcontroller, or other electronic components thatreceive and process electrical pulses or other signals generated by thephotosensor modules 26.

The radiation detection system 20 has a principal sensing area 222 thatcorresponds to the shape of the scintillating material. In theembodiment as illustrated in FIG. 2, the principle sensing area 222 hasa quadrilateral shape. In a particular embodiment, the shape can be asquare or other rectangle, a diamond, a trapezoid, or the like. Inanother embodiment, the principal sensing area 222 can have a differentshape, such as a circle, an oval, a triangle, a pentagon, a hexagon, orthe like. In still another embodiment, the principal sensing area 222may have an irregular shape.

In the embodiment illustrated in FIG. 2, the scintillation material 22can include a plurality of components. For example, the scintillationmaterial 22 can include a neutron sensing particulate material, such as³He, ⁶Li, or ¹⁰B (in ionized or non-ionized form). In an embodiment, the³He can be entrained or dissolved within a solid material. Uponreceiving a thermal neutron, the neutron sensing particulate materialcan produce a secondary particle, such as an alpha particle and tritonparticle, in response to receiving the thermal neutron. In anembodiment, the secondary particle can include a positively chargedparticle, such as an alpha particle (⁴He nucleus), a triton particle (³Hnucleus), a deuteron particle (²H nucleus), a ⁷Li nucleus, or anycombination thereof. The scintillation material 22 can also include ascintillating particulate material, such as ZnS, CaWO₄, Y₂SiO₅, ZnO,ZnCdS, CaF₂, yttrium aluminum garnet (“YAG”), yttrium aluminumperovskite (“YAP”), bismuth germanate (“BGO”), gadoliniumoxyorthosilicate (“GSO”), or another substance to produce photons inresponse to receiving secondary particles.

In a particular embodiment, the scintillating particulate material mayhave a low sensitivity to gamma radiation. As used herein, sensitivityrefers to the absorption efficiency of the target radiation. As such, ascintillating particulate material with low sensitivity to gamma photonshas a low absorption efficiency for gamma radiation. In the particularembodiment, the scintillating particulate material can have a gamma rayattenuation length of at least approximately 2.34 cm at 662 keV. Thus,the scintillating material 22 can detect neutrons without generating asignificant amount of noise due to gamma radiation. Utilizing onlyelements having a low atomic number, such as below 50, even below 40,can reduce the sensitivity to gamma photons. For example, thescintillating particulate material 22 can incorporate a ZnS, a ZnO, aZnCdS, a YAG, a YAP, a CaF₂, or any combination thereof. Additionally,the scintillating particulate material 22 can include a dopant, such asa transition metal, a rare earth metal, or another metal. For example,the scintillation particulate material 22 can include ZnS:Ag, ZnS:Cu,ZnS:Ti, Y₂SiO₅:Ce, ZnO:Ga, or ZnCdS:Cu.

In an embodiment, the neutron sensing particulate material and ascintillating particulate material can be dispersed within a polymermatrix. The polymer matrix can include poly(vinyl toluene) (“PVT”), apolystyrene (“PS”), a poly(methyl methacrylate) (“PMMA”), or anycombination thereof. The scintillation material 22 can be in the form ofa cast sheet or another suitable form. When the scintillating material22 is in the form of fibers, the fibers can have cross sections that aresubstantially rectangular, substantially round, or another shape. Inanother particular embodiment, an additional cladding may be used, suchas a fluoropolymer. In another particular embodiment, the scintillatingmaterial 22 can include a cast sheet. The scintillating material 22 maybe disposed along one side or opposite sides of the optical fibers.

In a non-limiting embodiment, the radiation detection system 20 of FIG.2 can include a thermalyzer to convert fast neutrons into thermalneutrons, for which ³He, ⁶Li, and ¹⁰B have greater cross-sections. Thethermalyzer can include a hydrocarbon or other thermalyzing material,such as a hydrogen-rich plastic material surrounding a portion of theradiation detection system 20, a plastic compound, another hydrocarboncompound, another material known to be an effective thermalyzer, or anycombination thereof. In a particular embodiment, the polymer matrix canbe a thermalyzer when the polymer matrix includes PMMA or otherhydrogen-rich polymer. In another embodiment, the thermalyzer may belocated at a suitable location between a radiation source (notillustrated, outside the radiation detection system 20) and thescintillation material 22.

The optical fibers include optical fibers 242, 244, and 246 and can havecross sections that are substantially rectangular (including square),substantially round, or another shape. Additional optical fibers arepresent within the principal sensing area but are not labeled orillustrated in FIG. 2. In an embodiment, the optical fibers may bespaced uniformly or nonuniformly within the principal sensing area 222.Optical fiber 242 is a centermost optical fiber that is disposedadjacent to the center of the principal sensing area 222. In aparticular embodiment, the optical fiber 242 is the optical fiberclosest to the center of the principal sensing area 222. Optical fiber246 is an outermost optical fiber that is disposed adjacent to theperimeter of the principal sensing area 222, that is, furthest from thecenter of the principal sensing area 222. Optical fiber 244 is disposedbetween the optical fibers 242 and 246.

The optical fiber 242 does not have an S-shaped bend, and the opticalfibers 244 and 246 include S-shaped bends 248. In a particularembodiment, the S-shaped bends are used to transmit light from the outerportions of the principal sensing area 222 to the photosensor modules 26that are disposed along a center line, such as a central axis generallydefined by the shapes of the photosensor modules 26. Particularembodiments described in more detail below can help to reduce photontransmission loss through the S-shaped bends 248 and provide betterlight collection uniformity between optical fibers, and particularlybetween the optical fibers 242 and 246. The composition of the opticalfibers and materials adjacent to the optical fibers are discussed inmore detail later in this specification.

Each photosensing module 26 can include one or more photomultipliertubes, solid-state photomultipliers (for example, Si-photomultipliers),or the like. In a particular embodiment, only one photosensor module 26may be used. In still another embodiment, more than two photosensormodules 26 may be used. In a particular embodiment, an optical fiber maybe optically coupled to a photomultiplier tube or solid-statephotomultiplier, and a different optical fiber may be optically coupledto the same or a different photomultiplier tube or solid-statephotomultiplier. In a further particular embodiment, a photosensingmodule 26 can include photomultiplier tubes or solid-statephotomultipliers organized into an array.

The geometric arrangement of the radiation detection system 20 asdescribed with respect to FIG. 2 can be substantially the same as thegeometric arrangement of the radiation detection system 10 of FIG. 1.Even with substantially the same overall geometric arrangement (forexample, size of the principal sensing area, optical fibers with orwithout S-shaped bends, positional relationships between optical fibersand the photosensor modules, and the like), the radiation detectionsystem 20 can have reduced photon transmission loss for S-shaped bends,improved light collection uniformity between optical fibers, andimproved light collection efficiency of optical fibers, as compared tothe radiation detection system 10. FIGS. 3 to 5 include differentcombinations of optical fibers and optical coupling materials that canimprove performance of the radiation detection system 20.

FIG. 3 includes an illustration of a cross sectional view of a portion aradiation detection system including the scintillating material 22,optical fibers 34, and an optical coupling material 36 that opticallycouples the scintillating material 22 to the optical fibers 34. In theembodiment as illustrated, the scintillating material 22 is disposedalong opposite sides of the optical coupling material 36. Each of theoptical fibers 34 consists essentially of a core 344. Unlike the opticalfibers 14 in FIG. 1, the optical fibers 34 do not include claddingsurrounding the optical core 344. In the embodiment as illustrated, theoptical coupling material 36 directly contacts the cores 344 of theoptical fibers 34. In this embodiment, the optical coupling material 36is the only material disposed between two immediately adjacent cores 344within the principal sensing area 222. In the embodiment as illustrated,the optical coupling material 36 directly contacts the scintillatingmaterial 22.

The refractive index of the optical coupling material 36 is less thanthe refractive index of the cores 344. In a particular embodiment, therefractive index (η) of the optical coupling material 36 is not greaterthan 1.60, in another embodiment, not greater than 1.50, and in afurther embodiment is not greater than 1.45. In a particular embodiment,the refractive index of the optical core is at least 1.50, in anotherembodiment, at least 1.55, and in a further embodiment is at least 1.60.

The optical coupling material 36 can include a silicone rubber (η=1.42)or a polymer. In a particular embodiment, the polymer can include PMMA(η=1.49) or poly(ethyl acrylate) (η=1.49). The core can include PS(η=1.60), PVT (η=1.59), or PMMA. In an embodiment using a relativelyhigh difference between the refractive indices, the optical couplingmaterial 36 includes a silicone rubber, and the core 344 includes PS.

FIG. 4 includes an illustration of a cross-sectional view of a portion aradiation detection system including the scintillating material 22,optical fibers 44, an optical coupling material 46, and a fluid 48between the optical fibers 44. The composition and refractive indicesfor the optical fibers 44, including optical cores 444, and the opticalcoupling materials 46 can be any of those previously described withrespect to the optical fibers 34, including optical cores 344, and theoptical coupling material 36. The fluid 48 can have a refractive indexthat is significantly less as compared to many solids. Gases typicallyhave lower refractive indices as compared to liquids. Many gases have arefractive index of 1.00. An exemplary gas that can be used includesair, a noble gas, CO₂, N₂, or the like. Air can include water vapor ormay be substantially free of water vapor, such as clean dry air. Thenoble gas may be present in the fluid 48 at a concentration higher thanAr in air (0.9 volume %). In an embodiment, the noble gas may be atleast 2 volume % of the fluid 48. Similarly, CO₂ and N₂ can be presentat concentrations different from their respective concentrations in air(0.03 volume % for CO₂, and 78 volume % for N₂). For example, fluid 48can include at least 0.1 volume % CO₂, less than 75 volume % N₂, or atleast 80 volume % N₂. In a particular embodiment, the fluid 48 caninclude at least 10 volume %, at least 50 volume %, or at least 99volume % of any foregoing gas or combination of such gases.

In another embodiment, more rigidity between optical fibers 44 may beneeded or desired. In this embodiment, an aerogel may be used betweenthe optical fibers 44. Aerogel includes a significant amount ofentrained gas, and thus, the fluid 48 can include the entrained gas. Ina particular embodiment, the aerogel can include a silica aerogel andhave a refractive index in a range of 1.05 to 1.10. Compare silicaaerogel to glass, which is a substantially solid material that has arefractive index of 1.46 when it consists essentially of SiO₂ and higherrefractive indices when dopants or other impurities are added to theSiO₂. In still a further embodiment, the principal sensing area of theradiation detection system may be used in a high pressure environment.The fluid 48 may include a substantially incompressible fluid, such as aliquid. In an embodiment, the liquid can include water or an organiccompound. In a particular embodiment, the liquid can consist essentiallyof water (η=1.33), such as distilled water or tap water. In anotherembodiment, the liquid can be an aqueous solution. An exemplary aqueoussolution can include a salt or an acid (mineral or organic acid).Typically, as the concentration of the salt or acid increases, therefractive index also increases.

Some organic compounds have refractive indices below or close to therefractive index of water. In a particular embodiment, the organiccompound can include fluorine or a hydroxyl group. Exemplary organiccompounds can include CF₃COOH (η=1.28), CF₃CH₂OH (η=1.29), methanol(η=1.33), ethanol (η=1.36), another suitable organic compound, or anycombination thereof.

In a further embodiment, the fluid 48 can be a non-Newtonian fluid. Inan embodiment, the fluid 48 can be a gelatinous material at (1)atmospheric pressure and a temperature of approximately 20° C. or (2)the normal operating temperatures and pressures for the radiationdetection system. For example, the radiation detection system may beused outdoors at a border crossing. The normal operating temperaturescan be in a range of −50° C. to +70° C. and the normal operatingpressure can be approximately one atmosphere.

The material and physical states of those materials within the fluid 48may be selected such that the fluid 48 is compatible with the opticalfibers 44 and the optical coupling material 46, so that the fluid 48does not dissolve or adversely affect the optical fibers 44 or theoptical coupling material 46. After reading this specification, skilledartisans will be capable of selecting a fluid for a particular radiationdetection system.

FIG. 5 includes an illustration of a cross sectional view of a portionof a radiation detection system similar to the radiation detectionsystem as illustrated in FIG. 4. In FIG. 5, the radiation detectionsystem includes the scintillating material 22, optical fibers 54, anoptical coupling material 56, and a fluid 58 between the optical fibers54. The composition and refractive indices for the optical fibers 54,including optical cores 544, the optical coupling materials 56, and thefluid 58 can be any of those previously described with respect to theoptical fibers 34, including the optical cores 344, the optical couplingmaterial 36, and the fluid 48. In the embodiment as illustrated in FIG.5, the optical coupling material 56 and the optical cores 544 may notadhere or weakly adhere to each other. An adhesive layer 562 may bedisposed between and contact the optical coupling material 56 and theoptical cores 544 of the optical fibers 54. In an embodiment, theadhesive layer 562 has a refractive index that is about the same or lessthan the refractive index of the optical coupling material 56. In aparticular embodiment, the adhesive layer 562 can include poly(ethylacrylate) (η=1.47), poly(vinyl acrylate) (η=1.47), poly(vinyl butyral)(η=1.49), another suitable adhesive material, or any combinationthereof. In a particular embodiment, the adhesive layer 562 can compriseCYANOCRIL™ (available from American Cyanamid), which includes poly(ethylacrylate) or OPTICALLY CLEAR ADHESIVE 9483™, which includes an acryliccompound (available from 3M Company). An optional heat or curingoperation may be performed to improve adhesion.

In another embodiment (not illustrated), the adhesive layer 562 maysurround the optical cores 544 before the optical cores 544 are placednear the optical coupling material 56. In this embodiment, the adhesivelayer 562 is disposed along the sides of the optical cores 544, and thefluid 58 may directly contact the optical coupling material 56 atlocations spaced apart from the optical cores 544.

Radiation detection systems using optical fibers and optical couplingmaterials as described with respect to FIGS. 2 to 5 and theircorresponding embodiments can exhibit improved performance Photontransmission losses through S-shaped bends can be significantly reduced.FIG. 6 illustrates maps 610 and 640 of photons lost as light istransmitted through the S-shaped bends. The maps 610 and 640 correspondto top views of optical fibers, and thus, the scintillating material isnot illustrated in the maps 610 and 640. With respect to FIG. 6, thevertical distance for the bend is measured in a top-to-bottom direction,and the lateral distance for the bend is measured in a side-to-sidedirection. The ratio of the vertical distance to the lateral distance,which is herein referred to as the bend ratio, is 0.8 for both maps.

The map 610 corresponds to an optical fiber/optical coupling materialcombination as described with respect to FIG. 1. More particularly, theoptical fiber 14 is a PS core surrounded by a PMMA cladding, and theoptical coupling material 16 is epoxy. Hence, the PMMA cladding andepoxy are disposed along the sides of the PS core along the S-shapedbend. Hereinafter, this combination will be referred to as the “FIG. 1Combination.” The black dots along the map 610 depict locations wherephotons are lost during transmission. Referring to map 610, asignificant amount of photons are lost at and just after the opticalfiber 14 starts the bend and at and just after the inflection point. Forthe fiber/optical coupling material combination as described in thisparagraph, 44% of the photons entering the S-shaped bend are lost thoughthe S-shaped bend.

Map 640 corresponds to an optical fiber/optical coupling materialcombination as described with respect to FIG. 4. In a particularembodiment, the optical fiber 44 has a core 444 that is PS without anycladding material, the optical coupling material 46 is silicone rubber,and the fluid 48 is air, which is adjacent to the sides of the opticalfiber 44. Hence, air is disposed along the sides of the PS core alongthe S-shaped bend. Hereinafter, this combination will be referred to asthe “FIG. 4 Combination.” Referring to map 640, substantially fewerphotons are lost. Only 10% of the photons entering the S-shaped bend arelost though the S-shaped bend. Although not illustrated, an opticalfiber/optical coupling material combination can include a PS core andsilicone rubber as illustrated with respect to FIG. 3. Hereinafter, thiscombination will be referred to as the “FIG. 3 Combination,” and 25% ofthe photons entering the S-shaped bend are lost though the S-shapedbend. Thus, in an embodiment as described herein, not greater than 43%of the photons entering the S-shaped bend are lost though the S-shapedbend, and in another embodiment, not greater than 25% of the photonsentering the S-shaped bend are lost though the S-shaped bend. In aparticular embodiment, not greater than 10% of the photons entering theS-shaped bend are lost though the S-shaped bend.

The reduced photon transmission loss can help to improve the lightcollection uniformity between optical fibers. Referring to FIG. 2, theoptical fiber 242 is the centermost optical fiber and does not have anS-shaped bend, and therefore, does not have photon transmission losscaused by an S-shaped bend. The optical fiber 246 is the outermostoptical fiber and has the largest bend ratio for the S-shaped bend. In aparticular embodiment, the bend ratio of the S-bend is 0.8. As the bendratio increases, the photon transmission loss due to the S-shaped bendincreases, and as the bend ratio decreases, the photon transmissionloss, due to the shallower S-shaped bend, decreases. Thus, the opticalfiber 244 has a photon transmission loss due to the S-shaped bend thatis less than the optical fiber 246. Therefore, the light collectionuniformity is the percentage of the light exiting the optical fiber 246compared to the light exiting the optical fiber 242. For the purposes ofcomparison, the optical fibers 242 and 246 are exposed to the same lightflux from the scintillating material 22. For the FIG. 1 Combination, thelight collection uniformity between the optical fibers is only 76%.

In an embodiment, the light collection uniformity can be at least 77%,and in another embodiment, the light collection uniformity can be atleast 90%. In a particular embodiment, the FIG. 3 Combination has alight collection uniformity of 95%, and in another particularembodiment, the FIG. 4 Combination has a light collection uniformity of97%.

Radiation detection systems having a scintillating material and opticalfibers typically have a relatively low light collection efficiency. Thetable below compares the light collection efficiency for optical fibershaving the FIG. 1 Combination, the FIG. 3 Combination, and the FIG. 4Combination for different bend ratios of S-shaped bends. FIG. 7 includesa graph of light collection efficiency as a function of bend ratio forthe FIG. 1, FIG. 3, and FIG. 4 Combinations.

FIG. 1 FIG. 3 FIG. 4 Bend Ratio Combination Combination Combination 100.0 0.0 7.9 5 0.1 1.7 11.9 2.5 2.3 7.3 17.9 1.25 4.9 11.1 20.6 1 5.511.8 20.9 0.8 5.9 12.7 20.9 0.67 6.3 12.8 21.2 0.5 6.6 13.0 21.5 0.4 6.913.1 21.4 0.3 7.2 13.2 21.3 0.2 7.5 13.2 21.3 0.1 7.8 13.3 21.5 0 8.013.3 21.7

A few data points are addressed. At a bend ratio of 10, the FIG. 4Combination has a light collection efficiency of 7.9%, whereas the FIG.1 and FIG. 3 Combinations have no significant light collected. Thus, ina particular embodiment, at a bend ratio of 10, the light collectionefficiency is greater than zero. At a vertical:lateral ratio of 0.8, theFIG. 1 Combination has a light collection efficiency of 5.9%, the FIG. 3Combination has a light collection efficiency of 12.7%, and the FIG. 4Combination has a light collection efficiency of 20.9%. Accordingly, inan embodiment, at a bend ratio of 0.8, the light collection efficiencyis at least 6%. Even when the optical fiber has no S-shaped bend (bendratio of 0), the FIG. 1 Combination has a light collection efficiency ofonly 8.0%. The FIG. 3 Combination has a light collection efficiency of13.3%, and the FIG. 4 Combination has a light collection efficiency of21.7%. Thus, in an embodiment, without an S-shaped bend, the lightcollection efficiency is at least 9%.

On a relative basis, the FIG. 3 Combination has a light efficiency thatis at least 1.5 times greater than the FIG. 1 Combination, regardless ofbend ratio, and has a light efficiency that is more than 2 times greaterthan the FIG. 1 Combination at a bend ratio of at least 0.67. Theimprovement with the FIG. 4 Combination is even more pronounced. TheFIG. 4 Combination has a light efficiency that is at least 2.5 timesgreater than the FIG. 1 Combination, regardless of bend ratio, and has alight efficiency that is more than 5 times greater than the FIG. 1Combination at a bend ratio of at least 1.25.

Radiation detection systems in accordance with embodiments describedherein can have a higher signal:noise ratio. Due to less photontransmission loss through S-shaped bends, greater light collectionuniformity, greater light collection efficiency, or any combinationthereof, the signal:noise ratio for the radiation detector system isgreater than the signal:noise ratio of a conventional radiation systemhaving a similar overall geometry. For purposes of comparison, the tworadiation detection systems are substantially identical other thanoptical fibers, optical coupling material, and any material between theoptical fibers.

Many different test methodologies may be used to determine signal:noiseratio. The actual methodology may depend on the targeted radiation ofinterest, such as neutrons, gamma radiation, or another radiationsource. For gamma radiation, a gamma radiation source is placed near thesensing area of a radiation detection system. The signal:noise ratio forthe radiation detection system can be obtained by dividing a peakintensity, corresponding to radiation emitted by the gamma radiationsource, by an intensity approximately 10 to 500 ns after the time of thepeak intensity. Background noise corresponds to the intensityapproximately 10 to 500 ns after the time of the peak intensity.

For neutrons, two integrated signals can used to obtain a signal:noiseratio for a radiation detection system. The first integrated signal canbe obtained by integrating intensity over an energy from approximately20 keV to at least 100 keV when a neutron radiation source is placednear the sensing area of the radiation detection system. If desired, theintegration can be extended to an energy of 4.7 MeV or potentiallyhigher; however, the value of the integrated intensity does notsubstantially change as the energy is increased beyond 100 keV. Thesecond integrated signal can be obtained by integrating intensity oversubstantially the same energy range used for the first integratedsignal; however, the second integrated signal is obtained when there isno significant neutron or gamma radiation source near the sensing areaof the radiation detection system. Background noise corresponds to thesecond integrated signal. The signal:noise ratio can be obtained bydividing the first integrated signal by the second integrated signal.

Intensity can be measured in units of counts, bits, or another unit ofmeasure. Energy may correspond to a bin or a channel number of amultichannel analyzer. Other methodologies to obtain signal:noise ratiofor gamma radiation, neutrons, or for other targeted radiation.

When comparing two systems, the testing environments and methodologiesshould be substantially the same or at least as close as reasonablypossible. For example, the same radiation source used should be placedsubstantially the same distance from the center of the sensing area ofthe radiation detection system when testing each radiation detectionsystem being compared. For the gamma radiation test methodologydescribed above, the time difference between the peak intensity and theother intensity should be approximately the same. For example, the timedifference is approximately 100 ns when comparing the two systems. Forthe neutrons test methodology described above, the ending energy for theintegrated signals for both radiation detections systems should beapproximately the same. For example, the ending energy is approximately500 keV when comparing the two systems.

A conventional radiation detection system has the FIG. 1 Combination andthe novel radiation detection system has the FIG. 3 Combination, FIG. 4Combination, an optical fiber/optical coupling combination of FIG. 5, orany other optical fiber/optical coupling combination described withrespect to FIGS. 3 to 5. In a particular embodiment, the signal:noiseratio of the novel radiation detection system is at least two timesgreater than the signal:noise ratio of the conventional radiationdetection system, and in another particular embodiment, the signal:noiseratio of the novel radiation detection system is at least three timesgreater than the signal:noise ratio of the conventional radiationdetection system.

While the radiation detection systems described herein can be used todetect neutrons, gamma radiation, or both, the greater signal:noiseratio can be beneficial for distinguishing between neutrons and gammaradiation. Both neutrons and gamma radiation produce an intense primarypeak. Other than the primary peak, gamma radiation does not havesignificant secondary peaks spaced apart from the primary peak, andhence, other than the primary peak, the remainder of the spectrum forthe gamma radiation corresponds to noise. Unlike gamma radiation,neutrons produce secondary peaks that are spaced apart from the primarypeak; however, the secondary peaks are of substantially lower intensitythan primary peak. With a low signal:noise ratio, distinguishing thesecondary peaks from noise may be difficult and could result inincorrect classification of radiation. For example, a neutron may beclassified as gamma radiation and vice versa. When the signal:noiseratio is greater, the secondary peaks seen with neutrons will besignificantly higher than peaks seen with noise. Thus, the radiationdetection system may more accurately discriminate between neutrons andgamma radiation.

Although many of the embodiments have been directed to particularcompositions for optical fibers (for example, cores including PS),optical coupling materials (for example, silicone rubber), andpotentially a fluid (for example, air) between optical fibers, suchembodiments are described to allow a better comparison to a conventionalradiation detection system. Clearly, the other materials describedherein can be used. For example, if the optical fibers are to shift thelight to another color other than green, a different material for theoptical fibers may be used. If the optical core would include polyimide(η=1.70), the signal:noise ratio may be further improved. Theperformance of the radiation detection system with such other materialswill be different from the FIG. 3 Combination and the FIG. 4Combination; however, many of these other radiation detection systemsmay have superior characteristics compared to a conventional radiationdetection system.

Many different aspects and embodiments are possible. Some of thoseaspects and embodiments are described herein. After reading thisspecification, skilled artisans will appreciate that those aspects andembodiments are only illustrative and do not limit the scope of thepresent invention. Additionally, those skilled in the art willunderstand that some embodiments that include analog circuits can besimilarly implemented using digital circuits, and vice versa.

In a first aspect, a radiation detection system can include ascintillating material to produce a light in response to receiving atarget radiation, a first optical fiber and a second optical fiber thatare coupled to the scintillating material, and a fluid is disposedbetween the first and second optical fibers.

In an embodiment of the first aspect, the fluid includes a gas. In aparticular embodiment, the fluid includes air. In a more particularembodiment, the air is substantially free of water vapor. In anotherparticular embodiment, the fluid includes at least 2 volume % of a noblegas. In a still another particular embodiment, the fluid includes atleast 0.1 volume % of CO₂. In yet another particular embodiment, thefluid includes less than 75 volume % or at least 80 volume % N₂. In afurther particular embodiment, the gas is disposed within an aerogel. Ina more particular embodiment, the aerogel includes a silica aerogel.

In another embodiment of the first aspect, the fluid is a substantiallyincompressible fluid. In still another embodiment, the fluid includes aliquid. In a particular embodiment, the liquid includes water. Inanother particular embodiment, the liquid includes an organic compound.In a yet another embodiment, the fluid includes a non-Newtonian fluid.In a particular embodiment, the non-Newtonian fluid includes agelatinous material at (i) atmospheric pressure and a temperature ofapproximately 20° C., (ii) normal operating temperature and pressure forthe radiation detection system, or both (i) and (ii).

In a further embodiment of the first aspect, the fluid has a refractiveindex lower than a refractive index of a core of the first or secondoptical fiber. In still a further embodiment, the fluid has a refractiveindex lower than refractive indices of cores of the first and secondoptical fibers. In yet a further embodiment, a core of the first orsecond optical fiber includes a polystyrene, a polyvinyl toluene, apolyacrylate, or any combination thereof. In another embodiment, a coreof the first optical fiber and a core of the second optical fiber havesubstantially a same composition.

In still another embodiment of the first aspect, the first optical fiberincludes an S-shaped bend. In a particular embodiment, the secondoptical fiber does not include an S-shaped bend. In another particularembodiment, the radiation detection system is configured such that theS-shaped bend has a bend ratio of approximately 0.8, and the firstoptical fiber has a photon transmission loss through the S-bend of notgreater than 43%. In a more particular embodiment, the photontransmission loss is not greater than 25% or not greater than 10%.

In a further embodiment of the first aspect, the scintillating material,the first and second fibers, and the fluid are disposed within aprincipal sensing area of the radiation detection system. In aparticular embodiment, the first optical fiber is an outermost opticalfiber disposed adjacent to a perimeter of the principal sensing area,the second optical fiber is a centermost optical fiber disposed adjacentto a center of the principal sensing area, and light collectionuniformity between the first and second optical fibers is at least 77%.In a more particular embodiment, the light collection uniformity is atleast 90% or at least 95%.

In another particular embodiment of the first aspect, the radiationdetection system has a first signal:noise ratio. A different radiationdetection systems is substantially identical to the radiation system,except that the different radiation detection system includes opticalfibers and epoxy as an only material disposed between and in directcontact with the optical fibers within a principal sensing area of thedifferent radiation detection system, wherein each optical fiberconsists of a polystyrene core and a poly(methyl methacrylate) claddingsurrounding the polystyrene core. The different radiation detectionsystem has a second signal:noise ratio less than the first signal:noiseratio. In an even more particular embodiment, the first signal:noiseratio is at least two times greater than the second signal:noise ratioor at least three times greater than the second signal:noise ratio.

In yet a further embodiment of the first aspect, the radiation detectionsystem further includes an optical coupling material disposed betweenthe scintillating material and the first or second optical fiber. In aparticular embodiment, the optical coupling material directly contacts acore of the first or second optical fiber. In another particularembodiment, the radiation detection system further includes an adhesivematerial, wherein the adhesive material is disposed between and indirect contact with the optical coupling material and a core of thefirst or second optical fiber. In still another particular embodiment,the optical coupling material has a refractive index that is less than arefractive index of a core of the first or second optical fiber. In amore particular embodiment, the optical coupling material includessilicone rubber. In another more particular embodiment, the opticalcoupling material includes a polymer. In an even more particularembodiment, the polymer includes a polyacrylate, a poly(vinyl toluene),or any combination thereof.

In still a further embodiment of the first aspect, the target radiationincludes neutrons, gamma radiation, or any combination thereof. In yet afurther embodiment, the radiation detection system further includes aphotosensor module optically coupled to ends of the first and secondoptical fibers. In a particular embodiment, the photosensor moduleincludes a photomultiplier tube or a solid-state photomultiplier. Inanother particular embodiment, the photosensor module includes a firstphotosensor component coupled to the first optical fiber and a secondphotosensor component coupled to the second optical fiber.

In a second aspect, a radiation detection system can include ascintillating material to produce a light in response to receiving atarget radiation, a first optical fiber and a second optical fiber, andan optical coupling material disposed between the first and secondoptical fibers, wherein the optical coupling material has a refractiveindex less than 1.50.

In an embodiment of the second aspect, the optical coupling material isin direct contact with cores of the first and second optical fibers. Inanother embodiment, an adhesive layer is disposed between the opticalcoupling material and a core of the first or second optical fiber. In aparticular embodiment, the adhesive layer has a refractive index lessthan the core of the first or second optical fiber. In anotherparticular embodiment, the adhesive layer includes a poly(vinylalcohol), a polyacrylate, a poly(vinyl butyral), or any combinationthereof. In still another embodiment, the optical coupling materialincludes a polymer. In a more particular embodiment, the polymerincludes a polyacrylate. In yet another embodiment, the optical couplingmaterial includes an aerogel. In a particular embodiment, the opticalcoupling material includes a silica aerogel.

In a further embodiment of the second aspect, a core of the first orsecond optical fiber includes a polystyrene, a poly(vinyl toluene), apolyacrylate, or any combination thereof. In still a further embodiment,the optical coupling material is disposed between the scintillatingmaterial and each of the first and second optical fibers. In anotherembodiment, the first and second optical fibers have substantially asame composition. In a still another embodiment, the first optical fiberincludes an S-shaped bend. In a particular embodiment, the secondoptical fiber does not include an S-shaped bend. In another particularembodiment, the radiation detection system is configured such that theS-shaped bend has a bend ratio of approximately 0.8, and the firstoptical fiber has a photon transmission loss through the S-bend of notgreater than 43%. In a more particular embodiment, the photontransmission loss is not greater than 25% or not greater than 10%. Inyet another embodiment, the first optical fiber is an outermost opticalfiber disposed adjacent to a perimeter of a principal sensing area, thesecond optical fiber is a centermost optical fiber disposed adjacent toa center of the principal sensing area, and a light collectionuniformity between the first and second optical fibers is at least 77%.In a particular embodiment, the light collection uniformity is at least90% or at least 95%.

In a further embodiment of the second aspect, the radiation detectionsystem has a first signal:noise ratio. A different radiation detectionsystems is substantially identical to the radiation system, except thatthe different radiation detection system includes optical fibers andepoxy as an only material disposed between and in direct contact withthe optical fibers within a principal sensing area of the differentradiation detection system, wherein each optical fiber consists of apolystyrene core and a poly(methyl methacrylate) cladding surroundingthe polystyrene core. The different radiation detection system has asecond signal:noise ratio less than the first signal:noise ratio. In aparticular embodiment, the first signal:noise ratio is at least twotimes greater than the second signal:noise ratio or at least three timesgreater than the second signal:noise ratio. In still a furtherembodiment, the optical coupling material is disposed between thescintillating material and the first or second optical fiber. In yet afurther embodiment, the optical coupling material includes siliconerubber. In a particular embodiment, the optical coupling materialincludes a polymer. In a more particular embodiment, the polymerincludes a polyacrylate.

In another embodiment of the second aspect, the radiation detectionsystem further includes a photosensor module optically coupled to endsof the first and second optical fibers. In a particular embodiment, thephotosensor module includes a photomultiplier tube or a solid-statephotomultiplier. In another particular embodiment, the photosensormodule includes a first photosensor component coupled to the firstoptical fiber and a second photosensor component coupled to the secondoptical fiber. In still another embodiment, the optical couplingmaterial has a refractive index not greater than 1.45, or anothermaterial is disposed between first and second optical fibers and has arefractive index not greater than 1.45. In a further embodiment, theoptical coupling material has a refractive index not greater than 1.40,or another material is disposed between first and second optical fibersand has a refractive index not greater than 1.40. In still a furtherembodiment, the optical coupling material has a refractive index notgreater than 1.25, or another material is disposed between first andsecond optical fibers and has a refractive index not greater than 1.25.

In a third aspect, a radiation detection system can include ascintillating material to produce a light in response to receiving atarget radiation, optical fibers, and an optical coupling materialdisposed between scintillating material and the optical fibers. Theradiation detection system can have a first signal:noise ratio. Adifferent radiation detection systems is substantially identical to theradiation system, except that the different radiation detection systemincludes optical fibers and epoxy as an only material disposed betweenand in direct contact with the optical fibers within a principal sensingarea of the different radiation detection system, wherein each opticalfiber consists of a polystyrene core and a poly(methyl methacrylate)cladding surrounding the polystyrene core. The different radiationdetection system can have a second signal:noise ratio less than thefirst signal:noise ratio.

In an embodiment of the third aspect, the first signal:noise ratio is atleast two times greater than the second signal:noise ratio or at leastthree times greater than the second signal:noise ratio. In anotherembodiment, the target radiation includes neutrons, gamma radiation, orany combination thereof. In still another embodiment, the radiationdetection system further includes a photosensor module optically coupledto ends of the first and second optical fibers. In a particularembodiment, the photosensor module includes a photomultiplier tube or asolid-state photomultiplier. In another particular embodiment, thephotosensor module includes a first photosensor component coupled to thefirst optical fiber and a second photosensor component coupled to thesecond optical fiber.

In a fourth aspect, a radiation detection system can include ascintillating material to produce a light in response to receiving atarget radiation, an optical fiber, and an optical coupling materialdisposed between scintillating material and the optical fiber. Theoptical fiber may not have an S-shaped bend and has a light collectionefficiency of at least 9%, the optical fiber can have an S-shaped bendhas a bend ratio of 0.8 and a light collection efficiency of at least6%, or the optical fiber has an S-shaped bend can have a bend ratio of10 and a light collection efficiency greater than zero.

In an embodiment of the fourth aspect, the target radiation includesneutrons, gamma radiation, or any combination thereof. In anotherembodiment, the radiation detection system further includes aphotosensor module optically coupled to end of the optical fiber. In aparticular embodiment, the photosensor module includes a photomultipliertube or a solid-state photomultiplier.

In a fifth aspect, a method of using a radiation detection system caninclude placing a radiation source near the radiation detection systemcan include a scintillating material, a first optical fiber and a secondoptical fiber that are coupled to the scintillating material, whereinthe first optical fiber is an outermost optical fiber disposed adjacentto a perimeter of the principal sensing area, and the second opticalfiber is a centermost optical fiber disposed adjacent to a center of theprincipal sensing area. The method can also include generating a firstlight within the scintillating material and receiving at the first andsecond optical fibers first light from the scintillating material. Themethod can further include transmitting a second light to ends of thefirst and second optical fibers, wherein at substantially a same lightflux of the first light received at the first and second optical fibers,a light intensity at the end of the first optical fiber is at least 77%of a light intensity at the end of the second optical fiber.

In an embodiment of the fifth aspect, the light intensity at the end ofthe first optical fiber is at least 90% of the light intensity at theend of the second optical fiber. In another embodiment, the lightintensity at the end of the first optical fiber is at least 95% of thelight intensity at the end of the second optical fiber. In still anotherembodiment, the first optical fiber has an S-shaped bend. In aparticular embodiment, the second optical fiber does not have an S-bend.In another particular embodiment, the S-shaped bend has a bend ratio ofapproximately 0.8, and not greater than 43% of photons entering theS-shaped bend are lost during transmission through the S-bend. In a moreparticular embodiment, not greater than 25% of photons entering theS-shaped bend are lost during transmission through the S-bend. Inanother more particular embodiment, not greater than 10% of photonsentering the S-shaped bend are lost during transmission through theS-bend.

In yet another embodiment of the fifth aspect, the target radiationincludes neutrons, gamma radiation, or any combination thereof. In afurther embodiment, the radiation detection system further includes aphotosensor module optically coupled to the ends of the first and secondoptical fibers. In a particular embodiment, the photosensor moduleincludes a photomultiplier tube or a solid-state photomultiplier. Inanother particular embodiment, the photosensor module includes a firstphotosensor component coupled to the first optical fiber and a secondphotosensor component coupled to the second optical fiber.

In a sixth aspect, a method of using a radiation detection system caninclude placing a radiation source near the radiation detection systemincluding a scintillating material, and an optical fiber having anS-shaped bend that has a bend ratio of approximately 0.8. The method canalso include generating light within the scintillating material andreceiving at the optical fiber light from the scintillating material.The method can further include transmitting the light through theS-shaped bend of the first optical fiber, wherein not greater than 43%of photons entering the S-shaped bend are lost during transmissionthrough the S-bend.

In an embodiment of the sixth aspect, not greater than 25% of photonsentering the S-shaped bend are lost during transmission through theS-bend. In another embodiment, not greater than 10% of photons enteringthe S-shaped bend are lost during transmission through the S-bend. Instill another embodiment, the target radiation includes neutrons, gammaradiation, or any combination thereof. In a further embodiment, theradiation detection system further includes a photosensor moduleoptically coupled to an end of the optical fiber. In a particularembodiment, the photosensor module includes a photomultiplier tube or asolid state photomultiplier.

Note that not all of the activities described above in the generaldescription or the examples are required, that a portion of a specificactivity may not be required, and that one or more further activitiesmay be performed in addition to those described. Still further, theorder in which activities are listed is not necessarily the order inwhich they are performed.

In a particular embodiment, a method may be described in a series ofsequential actions. The sequence of the actions and the party performingthe actions may be changed without necessarily departing from the scopeof the teachings unless explicitly stated to the contrary. Actions maybe added, deleted, or altered. Also, a particular action may beiterated. Further, actions within a method that are disclosed as beingperformed in parallel may in particular cases be performed serially, andother actions within a method that are disclosed as being performedserially may in particular cases be performed in parallel.

Benefits, other advantages, and solutions to problems have beendescribed above with regard to specific embodiments. However, thebenefits, advantages, solutions to problems, and any feature(s) that maycause any benefit, advantage, or solution to occur or become morepronounced are not to be construed as a critical, required, or essentialfeature of any or all the claims.

The specification and illustrations of the embodiments described hereinare intended to provide a general understanding of the structure of thevarious embodiments. The specification and illustrations are notintended to serve as an exhaustive and comprehensive description of allof the elements and features of apparatus and systems that use thestructures or methods described herein. Separate embodiments may also beprovided in combination in a single embodiment, and conversely, variousfeatures that are, for brevity, described in the context of a singleembodiment, may also be provided separately or in any subcombination.Further, reference to values stated in ranges includes each and everyvalue within that range. Many other embodiments may be apparent toskilled artisans only after reading this specification. Otherembodiments may be used and derived from the disclosure, such that astructural substitution, logical substitution, or another change may bemade without departing from the scope of the disclosure. Accordingly,the disclosure is to be regarded as illustrative rather thanrestrictive.

1. A radiation detection system comprising: a scintillating material toproduce a light in response to receiving a target radiation; a firstoptical fiber and a second optical fiber that are coupled to thescintillating material; and a fluid is disposed between the first andsecond optical fibers.
 2. The radiation detection system of claim 1,wherein the fluid includes a gas.
 3. The radiation detection system ofclaim 2, wherein the fluid includes air.
 4. The radiation detectionsystem of claim 3, wherein the air is substantially free of water vapor.5. The radiation detection system of claim 2, wherein the fluid includesat least 2 volume % of a noble gas.
 6. The radiation detection system ofclaim 2, wherein the fluid includes at least 0.1 volume % of CO₂.
 7. Theradiation detection system of claim 2, wherein the fluid includes lessthan 75 volume % or at least 80 volume % N₂.
 8. The radiation detectionsystem of claim 2, wherein the gas is disposed within an aerogel.
 9. Theradiation detection system of claim 8, wherein the aerogel comprises asilica aerogel.
 10. The radiation detection system of claim 1, whereinthe fluid is a substantially incompressible fluid.
 11. The radiationdetection system of claim 1, wherein the fluid includes a liquid. 12.The radiation detection system of claim 11, wherein the liquid includeswater.
 13. The radiation detection system of claim 11, wherein theliquid includes an organic compound.
 14. The radiation detection systemof claim 1, wherein the fluid includes a non-Newtonian fluid.
 15. Theradiation detection system of claim 14, wherein the non-Newtonian fluidincludes a gelatinous material at (i) atmospheric pressure and atemperature of approximately 20° C., (ii) normal operating temperatureand pressure for the radiation detection system, or both (i) and (ii).16. The radiation detection system of claim 1, wherein the fluid has arefractive index lower than a refractive index of a core of the first orsecond optical fiber.
 17. The radiation detection system of claim 1,wherein the fluid has a refractive index lower than refractive indicesof cores of the first and second optical fibers.
 18. The radiationdetection system of claim 1, wherein a core of the first or secondoptical fiber includes a polystyrene, a polyvinyl toluene, apolyacrylate, or any combination thereof.
 19. The radiation detectionsystem of claim 1, wherein a core of the first optical fiber and a coreof the second optical fiber have substantially a same composition. 20.The radiation detection system of claim 1, wherein the first opticalfiber includes an S-shaped bend.
 21. The radiation detection system ofclaim 20, wherein the second optical fiber does not include an S-shapedbend.
 22. The radiation detection system of claim 20, wherein theradiation detection system is configured such that the S-shaped bend hasa bend ratio of approximately 0.8, and the first optical fiber has aphoton transmission loss through the S-bend of not greater than 43%. 23.The radiation detection system of claim 22, wherein the photontransmission loss is not greater than 25%.
 24. The radiation detectionsystem of claim 22, wherein the photon transmission loss is not greaterthan 10%.
 25. The radiation detection system of claim 1, wherein thescintillating material, the first and second fibers, and the fluid aredisposed within a principal sensing area of the radiation detectionsystem.
 26. The radiation detection system of claim 25, wherein: thefirst optical fiber is an outermost optical fiber disposed adjacent to aperimeter of the principal sensing area; the second optical fiber is acentermost optical fiber disposed adjacent to a center of the principalsensing area; and a light collection uniformity between the first andsecond optical fibers is at least 77%.
 27. The radiation detectionsystem of claim 26, wherein the light collection uniformity is at least90%.
 28. The radiation detection system of claim 26, wherein the lightcollection uniformity is at least 95%.
 29. The radiation detectionsystem of claim 25, wherein: the radiation detection system has a firstsignal:noise ratio; a different radiation detection systems issubstantially identical to the radiation system, except that thedifferent radiation detection system includes optical fibers and epoxyas an only material disposed between and in direct contact with theoptical fibers within a principal sensing area of the differentradiation detection system, wherein each optical fiber consists of apolystyrene core and a poly(methyl methacrylate) cladding surroundingthe polystyrene core; and the different radiation detection system has asecond signal:noise ratio less than the first signal:noise ratio. 30.The radiation detection system of claim 29, wherein the firstsignal:noise ratio is at least two times greater than the secondsignal:noise ratio.
 31. The radiation detection system of claim 29,wherein the first signal:noise ratio is at least three times greaterthan the second signal:noise ratio.
 32. The radiation detection systemof claim 29, further comprising an optical coupling material disposedbetween the scintillating material and the first or second opticalfiber.
 33. The radiation detection system of claim 32, wherein theoptical coupling material directly contacts a core of the first orsecond optical fiber.
 34. The radiation detection system of claim 32,further comprising an adhesive material, wherein the adhesive materialis disposed between and in direct contact with the optical couplingmaterial and a core of the first or second optical fiber.
 35. Theradiation detection system of claim 32, wherein the optical couplingmaterial has a refractive index that is less than a refractive index ofa core of the first or second optical fiber.
 36. The radiation detectionsystem of claim 35, wherein the optical coupling material comprisessilicone rubber.
 37. The radiation detection system of claim 35, whereinthe optical coupling material comprises a polymer.
 38. The radiationdetection system of claim 37, wherein the polymer comprises apolyacrylate, a poly(vinyl toluene), or any combination thereof.
 39. Theradiation detection system of claim 1, wherein the target radiationcomprises neutrons, gamma radiation, or any combination thereof.
 40. Theradiation detection system of claim 1, further comprising a photosensormodule optically coupled to ends of the first and second optical fibers.41. The radiation detection system of claim 40, wherein the photosensormodule comprises a photomultiplier tube.
 42. The radiation detectionsystem of claim 40, wherein the photosensor module comprises asolid-state photomultiplier.
 43. The radiation detection system of claim40, wherein the photosensor module comprises a first photosensorcomponent coupled to the first optical fiber and a second photosensorcomponent coupled to the second optical fiber.
 44. A radiation detectionsystem comprising: a scintillating material to produce a light inresponse to receiving a target radiation; a first optical fiber and asecond optical fiber; and an optical coupling material disposed betweenthe first and second optical fibers, wherein the optical couplingmaterial has a refractive index less than 1.50.
 45. The radiationdetection system of claim 44, wherein the optical coupling material isin direct contact with cores of the first and second optical fibers. 46.The radiation detection system of claim 44, wherein an adhesive layer isdisposed between the optical coupling material and a core of the firstor second optical fiber.
 47. The radiation detection system of claim 46,wherein the adhesive layer has a refractive index less than the core ofthe first or second optical fiber.
 48. The radiation detection system ofclaim 46, wherein the adhesive layer comprises a poly(vinyl alcohol), apolyacrylate, a poly(vinyl butyral), or any combination thereof.
 49. Theradiation detection system of claim 44, wherein the optical couplingmaterial comprises a polymer.
 50. The radiation detection system ofclaim 49, wherein the polymer comprises a polyacrylate.
 51. Theradiation detection system of claim 44, wherein the optical couplingmaterial comprises an aerogel.
 52. The radiation detection system ofclaim 51, wherein the optical coupling material comprises a silicaaerogel.
 53. The radiation detection system of claim 44, wherein a coreof the first or second optical fiber includes a polystyrene, apoly(vinyl toluene), a polyacrylate, or any combination thereof.
 54. Theradiation detection system of claim 44, wherein the optical couplingmaterial is disposed between the scintillating material and each of thefirst and second optical fibers.
 55. The radiation detection system ofclaim 44, wherein the first and second optical fibers have substantiallya same composition.
 56. The radiation detection system of claim 44,wherein the first optical fiber includes an S-shaped bend.
 57. Theradiation detection system of claim 56, wherein the second optical fiberdoes not include an S-shaped bend.
 58. The radiation detection system ofclaim 56, wherein the radiation detection system is configured such thatthe S-shaped bend has a bend ratio of approximately 0.8, and the firstoptical fiber has a photon transmission loss through the S-bend of notgreater than 43%.
 59. The radiation detection system of claim 58,wherein the photon transmission loss is not greater than 25%.
 60. Theradiation detection system of claim 58, wherein the photon transmissionloss is not greater than 10%.
 61. The radiation detection system ofclaim 44, wherein: the first optical fiber is an outermost optical fiberdisposed adjacent to a perimeter of a principal sensing area; the secondoptical fiber is a centermost optical fiber disposed adjacent to acenter of the principal sensing area; and a light collection uniformitybetween the first and second optical fibers is at least 77%.
 62. Theradiation detection system of claim 61, wherein the light collectionuniformity is at least 90%.
 63. The radiation detection system of claim61, wherein the light collection uniformity is at least 95%.
 64. Theradiation detection system of claim 44, wherein: the radiation detectionsystem has a first signal:noise ratio; a different radiation detectionsystems is substantially identical to the radiation system, except thatthe different radiation detection system includes optical fibers andepoxy as an only material disposed between and in direct contact withthe optical fibers within a principal sensing area of the differentradiation detection system, wherein each optical fiber consists of apolystyrene core and a poly(methyl methacrylate) cladding surroundingthe polystyrene core; and the different radiation detection system has asecond signal:noise ratio less than the first signal:noise ratio. 65.The radiation detection system of claim 64, wherein the firstsignal:noise ratio is at least two times greater than the secondsignal:noise ratio.
 66. The radiation detection system of claim 64,wherein the first signal:noise ratio is at least three times greaterthan the second signal:noise ratio.
 67. The radiation detection systemof claim 44, wherein the optical coupling material is disposed betweenthe scintillating material and the first or second optical fiber. 68.The radiation detection system of claim 44, wherein the optical couplingmaterial comprises silicone rubber.
 69. The radiation detection systemof claim 68, wherein the optical coupling material comprises a polymer.70. The radiation detection system of claim 69, wherein the polymercomprises a polyacrylate.
 71. The radiation detection system of claim44, further comprising a photosensor module optically coupled to ends ofthe first and second optical fibers.
 72. The radiation detection systemof claim 71, wherein the photosensor module comprises a photomultipliertube.
 73. The radiation detection system of claim 71, wherein thephotosensor module comprises a solid-state photomultiplier.
 74. Theradiation detection system of claim 71, wherein the photosensor modulecomprises a first photosensor component coupled to the first opticalfiber and a second photosensor component coupled to the second opticalfiber.
 75. The radiation detection system of claim 44, wherein: theoptical coupling material has a refractive index not greater than 1.45;or another material is disposed between first and second optical fibersand has a refractive index not greater than 1.45.
 76. The radiationdetection system of claim 44, wherein: the optical coupling material hasa refractive index not greater than 1.40; or another material isdisposed between first and second optical fibers and has a refractiveindex not greater than 1.40.
 77. The radiation detection system of claim44, wherein: the optical coupling material has a refractive index notgreater than 1.25; or another material is disposed between first andsecond optical fibers and has a refractive index not greater than 1.25.78. A radiation detection system comprising: a scintillating material toproduce a light in response to receiving a target radiation; opticalfibers; and an optical coupling material disposed between scintillatingmaterial and the optical fibers, wherein: the radiation detection systemhas a first signal:noise ratio; a different radiation detection systemsis substantially identical to the radiation system, except that thedifferent radiation detection system includes optical fibers and epoxyas an only material disposed between and in direct contact with theoptical fibers within a principal sensing area of the differentradiation detection system, wherein each optical fiber consists of apolystyrene core and a poly(methyl methacrylate) cladding surroundingthe polystyrene core; and the different radiation detection system has asecond signal:noise ratio less than the first signal:noise ratio. 79.The radiation detection system of claim 78, wherein the firstsignal:noise ratio is at least two times greater than the secondsignal:noise ratio.
 80. The radiation detection system of claim 78,wherein the first signal:noise ratio is at least three times greaterthan the second signal:noise ratio.
 81. The radiation detection systemof claim 78, wherein the target radiation comprises neutrons, gammaradiation, or any combination thereof.
 82. The radiation detectionsystem of claim 78, further comprising a photosensor module opticallycoupled to ends of the first and second optical fibers.
 83. Theradiation detection system of claim 82, wherein the photosensor modulecomprises a photomultiplier tube.
 84. The radiation detection system ofclaim 82, wherein the photosensor module comprises a solid-statephotomultiplier.
 85. The radiation detection system of claim 82, whereinthe photosensor module comprises a first photosensor component coupledto the first optical fiber and a second photosensor component coupled tothe second optical fiber.
 86. A radiation detection system comprising: ascintillating material to produce a light in response to receiving atarget radiation; an optical fiber; and an optical coupling materialdisposed between scintillating material and the optical fiber, wherein:the optical fiber does not have an S-shaped bend and has a lightcollection efficiency of at least 9%; the optical fiber has an S-shapedbend has a bend ratio of 0.8 and a light collection efficiency of atleast 6%; or the optical fiber has an S-shaped bend has a bend ratio of10 and a light collection efficiency greater than zero.
 87. Theradiation detection system of claim 86, wherein the target radiationcomprises neutrons, gamma radiation, or any combination thereof.
 88. Theradiation detection system of claim 86, further comprising a photosensormodule optically coupled to end of the optical fiber.
 89. The radiationdetection system of claim 88, wherein the photosensor module comprises aphotomultiplier tube.
 90. The radiation detection system of claim 88,wherein the photosensor module comprises a solid-state photomultiplier.91. A method of using a radiation detection system comprising: placing aradiation source near the radiation detection system comprising: ascintillating material; a first optical fiber and a second optical fiberthat are coupled to the scintillating material, wherein the firstoptical fiber is an outermost optical fiber disposed adjacent to aperimeter of the principal sensing area, and the second optical fiber isa centermost optical fiber disposed adjacent to a center of theprincipal sensing area; and generating a first light within thescintillating material; receiving at the first and second optical fibersfirst light from the scintillating material; and transmitting a secondlight to ends of the first and second optical fibers, wherein atsubstantially a same light flux of the first light received at the firstand second optical fibers, a light intensity at the end of the firstoptical fiber is at least 77% of a light intensity at the end of thesecond optical fiber.
 92. The method of claim 91, wherein the lightintensity at the end of the first optical fiber is at least 90% of thelight intensity at the end of the second optical fiber.
 93. The methodof claim 91, wherein the light intensity at the end of the first opticalfiber is at least 95% of the light intensity at the end of the secondoptical fiber.
 94. The method of claim 91, wherein the first opticalfiber has an S-shaped bend.
 95. The method of claim 94, wherein thesecond optical fiber does not have an S-bend.
 96. The method of claim94, wherein: the S-shaped bend has a bend ratio of approximately 0.8;and not greater than 43% of photons entering the S-shaped bend are lostduring transmission through the S-bend.
 97. The method of claim 96,wherein not greater than 25% of photons entering the S-shaped bend arelost during transmission through the S-bend.
 98. The method of claim 96,wherein not greater than 10% of photons entering the S-shaped bend arelost during transmission through the S-bend.
 99. The method of claim 91,wherein the target radiation comprises neutrons, gamma radiation, or anycombination thereof.
 100. The method of claim 91, wherein the radiationdetection system further comprises a photosensor module opticallycoupled to the ends of the first and second optical fibers.
 101. Themethod of claim 100, wherein the photosensor module comprises aphotomultiplier tube.
 102. The method of claim 100, wherein thephotosensor module comprises a solid-state photomultiplier.
 103. Themethod of claim 100, wherein the photosensor module comprises a firstphotosensor component coupled to the first optical fiber and a secondphotosensor component coupled to the second optical fiber.
 104. A methodof using a radiation detection system comprising: placing a radiationsource near the radiation detection system comprising: a scintillatingmaterial; an optical fiber having an S-shaped bend that has a bend ratioof approximately 0.8, generating light within the scintillatingmaterial; receiving at the optical fiber light from the scintillatingmaterial; and transmitting the light through the S-shaped bend of thefirst optical fiber, wherein not greater than 43% of photons enteringthe S-shaped bend are lost during transmission through the S-bend. 105.The method of claim 104, wherein not greater than 25% of photonsentering the S-shaped bend are lost during transmission through theS-bend.
 106. The method of claim 104, wherein not greater than 10% ofphotons entering the S-shaped bend are lost during transmission throughthe S-bend.
 107. The method of claim 104, wherein the target radiationcomprises neutrons, gamma radiation, or any combination thereof. 108.The method of claim 101, wherein the radiation detection system furthercomprises a photosensor module optically coupled to an end of theoptical fiber.
 109. The method of claim 108, wherein the photosensormodule comprises a photomultiplier tube.
 110. The method of claim 108,wherein the photosensor module comprises a solid state photomultiplier.